The Blues have been dealt a double blow with All Blacks prop Tony Woodcock and captain Luke Braid ruled out of Friday's crucial sudden-death derby with the Chiefs at Eden Park.

Woodcock suffered a shoulder injury during last week's loss to the Crusaders and with a six-day turnaround coach Sir John Kirwan felt he would not be fully fit and it was not worth risking him.

"Woody's had a great season for us so it's a big loss. He's been quite outstanding really and one of our best players since he's been back," Kirwan said.

"It's unfortunate but he's not quite 100 per cent and we need to make sure he's fine. I don't think it's too serious but it could be if he played with it and it's something he needs to get on top of."

In one of four changes, Sam Prattley replaces Woodcock at loosehead prop while Brendon O'Connor comes in for Braid, who has been carrying a shoulder injury all season and will undergo surgery tomorrow.

"He's been carrying a shoulder injury all year which has started to affect him quite badly. He missed the last Chiefs game because of it. He's been having issues so he needs to have double shoulder reconstruction," Kirwan said.

"We had two tentative dates booked, this week and the week after the finals and I just felt that if we could get it done now then he'd be back for the beginning of next season.

"It'll be quite a long recovery, the next date is a month away which would mean he'd miss the first month of next season and while we haven't given up hope of making the finals we've got a great guy to come in Brendon O'Connor so there's not too much of a loss from a technical point of view."

Charles Piutau returns to his favoured position of fullback in a reshuffled Blues backline, with Tevita Li coming onto the left wing in place of George Moala while Lolagi Visinia is hoping to overcome a haematoma to his quad and is currently bracketed with Moala.

Francis Saili also comes in at centre for Pita Ahki who has joined the New Zealand Sevens team ahead of the Commonwealth Games in Glasgow later this month.

"Pita Ahki has really grown this year and I think he's going to be a special player. It's really important to let guys follow their dreams and one of his dreams was to win a Commonwealth Games gold medal so we sat down and spoke about this about six weeks ago," Kirwan said.

"I spoke to Titch [Sevens coach Sir Gordon Tietjens] about it and the deal was if we were still travelling well I couldn't release him but if we were struggling a wee bit or out of the playoffs they could have him. On Sunday morning we weren't out of the playoffs so Pita wanted to play for us this weekend then go to the Sevens but I just felt that we've got a great player in Francis Saili who hasn't played a lot of footy this year and we don't lose a lot by letting Pita go and follow his dreams and help New Zealand get gold."

The Blues face the daunting challenge of having to beat back-to-back champion Chiefs by 38 points on Friday night while also denying them a bonus point to give themselves a chance of making the top six.

Kirwan is optimistic about his team's chances.

"I think we've improved as a rugby team this year. We're getting that consistency and we're still learning what it takes to be a winning franchise. If there's one team in this competition that can do it on Friday night it's us.

"We scored five tries in 25 minutes against the Lions and if things bounce our way we can score points like no other football team and when we're confident we're really scary. We got our bonus point after 18 minutes against the Force. Obviously this is a different football team we're coming up against on Friday but there's a lot for us to play for.

"The boys are very disappointed that we're not in the playoffs automatically, we're one point away from just having to just win the football game but we're up for the challenge."